The present invention relates to a signal generator which generates, in synchrony with the rotation of an engine, a crank angle reference signal containing a plurality of pulses representative of reference crank positions of cylinders. It also relates to an engine control apparatus using such a signal generator in which a plurality of cylinders of an engine are controlled on the basis of the plurality of pulses contained in the crank angle reference signal generated by the signal generator. More particularly, it relates to such an engine control apparatus which is able to improve the reliability in control by changing the reference crank positions in a practical control range in accordance with changes in the operating conditions of the engine.
In order for a multi-cylinder internal combustion engine such as used in automobiles to properly operate, fuel injection, ignition and the like for each cylinder must take place at prescribed rotational positions or angles of the crankshaft of the engine, i.e., at times when each piston of the engine is at a prescribed position with respect to top dead center. For this reason, an engine is equipped with a rotational position sensor such as a signal generator which senses the rotational angle or position of the crankshaft of the engine.
FIG. 5 illustrates, in a block diagram, a conventional control apparatus for a multi-cylinder internal combustion engine. The engine control apparatus includes a signal generator 8 which generates a positional signal L including a plurality of positional pulses corresponding to the respective cylinders of the engine, an interface circuit 9, and a control unit 10 in the form of a microcomputer which receives the positional signal L from the signal generator 8 through the interface circuit 9 and recognizes, based thereon, the operating condition (i.e., crank angle or rotational position) of each cylinder.
A typical example of such a signal generator 8 is illustrated in FIG. 6. In this figure, the signal generator 8 illustrated includes a rotating plate 2 mounted on a rotating shaft 1 (such as the distributor shaft) which rotates in synchrony with the crankshaft of the engine. The rotating plate 2 has a set of first slits 3a formed in it at prescribed locations. The slits 3a are disposed at equal intervals in the circumferential direction of the rotating plate 2. The slits 3a, which are equal in number to the cylinders, are disposed so as to correspond to prescribed rotational angles of the crankshaft and thus to prescribed positions of each piston with respect to top dead center for sensing when the crankshaft reaches a prescribed rotational position for each cylinder. Another or second slit 3b is formed in the rotating plate 2 adjacent one of the first slits 3a at a location radially inwardly thereof for sensing when the crankshaft rotational angle is such that the piston of a specific reference cylinder is in a prescribed position.
A first and a second light emitting diode 4a, 4b are disposed on one side of the rotating plate 2 on a first outer circle and a second inner circle, respectively, on which the outer slits 3a and the inner slits 3b are respectively disposed. A first and a second light sensor 5a, 5b each in the form of a photodiode are disposed on the other side of the rotating plate 2 in alignment with the first and the second light emitting diode 4a, 4b, respectively. The first light sensor 5a generates an output signal each time one of the outer slits 3a passes between the first light sensor 5a and the first light emitting diode 4a. Also, the second light sensor 5b generates an output signal each time the inner slit 3b passes between the second light sensor 5b and the second light emitting diode 4b. As shown in FIG. 7, the outputs of the first and second light sensors 5a, 5b are input to the input terminals of corresponding amplifiers 6a, 6b each of which has the output terminal coupled to the base of a corresponding output transistor 7a or 7b which has the open collector coupled to the interface circuit 9 (FIG. 5) and the emitter grounded.
Now, the operation of the above-described conventional engine control apparatus as illustrated in FIGS. 4 through 6 will be described in detail with particular reference to FIG. 8 which illustrates the waveforms of the output signals of the first and second light sensors 5a, 5b.
As the engine is operated to run, the rotating shaft 1 operatively connected with the crankshaft (not shown) is rotated together with the rotating plate 2 fixedly mounted thereon so that the first and second light sensors 5a, 5b of the signal generator 8 generate a first and a second signal L.sub.1, L.sub.2 each in the form of a square pulse. The first signal L.sub.1 is a crank angle signal called an SGT signal and has a rising edge corresponding to the leading edge of one of the outer slits 3a (i.e., a first prescribed crank angle or position of a corresponding piston) and a falling edge corresponding to the trailing edge thereof (i.e., a second prescribed crank angle of the corresponding piston). In the illustrated example, each square pulse of the SGT signal L.sub.1 rises at a crank angle of 75 degrees before top dead center (a first reference position B75) of each piston, and falls at a crank angle of 5 degrees before top dead center (a second reference position B5).
The second signal L.sub.2 is a cylinder recognition signal called an SGC signal, and has a rising edge corresponding to the leading edge of the inner slit 3b and a falling edge corresponding to the trailing edge thereof. The SGC signal L.sub.2 is issued substantially simultaneously with the issuance of an SGT signal pulse corresponding to the specific reference cylinder #1 so as to identify the same. To this end, the inner slit 3b is designed such that it has a leading edge corresponding to a crank angle before the first reference angle of the corresponding SGT signal pulse (i.e., a crank angle greater than 75 degrees before TDC), and a trailing edge corresponding to a crank angle after the second reference angle of the corresponding SGT signal pulse (i.e., a crank angle smaller than 5 degrees before TDC). Thus, actually, the rising edge of an SGC signal pulse occurs before that of a corresponding SGT signal pulse, and the falling edge of the SGC signal pulse occurs after that of the corresponding SGT signal pulse.
The two kinds of first and second signals L.sub.1, L.sub.2 thus obtained are input via the interface circuit 9 to the microcomputer 10 which identifies the specific reference cylinder #1 based on the second signal L.sub.2, and the operational positions (i.e., crank angles or rotational positions) of the remaining cylinders #2 through #4 based on the first signal L.sub.1, whereby various operational calculations and engine control operations such as for controlling ignition timing, fuel injection timing, etc., are properly performed. For example, the power supply to an unillustrated ignition coil is started by a timer after the lapse of a first predetermined time from the rising edge of a pulse of the first signal L.sub.1 (i.e., the reference position of 75 degrees before top dead center), and then it is cut off after the lapse of a second predetermined time therefrom. In this case, however, as the number of revolutions per minute of the engine increases, the ignition timing or power supply cut-off timing are advanced toward the reference position (i.e., 75 degrees BTDC) so that the length of time from the start of the power supply to the cut-off thereof decreases. Therefore, it is desirous that the reference position for control also be properly advanced from the crank angle reference position or the rising edge of a pulse of the first signal. To this end, each of the slits 3a in the rotary disk 2 must have an extended circumferential length, which, however, reduces the mechanical strength of the rotary disk 2. Moreover, the power supply to the ignition coil during a bypass ignition period (i.e., during early stages of an engine starting operation) is started at the first reference crank position or the rising edge of a first signal pulse (i.e., at 75 degrees BTDC), and it is cut off at the second reference crank position or the falling edge of the first signal pulse (i.e., at 5 degrees BTDC). Under this condition, if the first reference position for starting the power supply is set to a crank position advanced from 75 degrees BTDC so as to be able to increase the power supply time during high-speed operation of the engine, power consumption increases and great heat is generated at the ignition coil and its related elements during a bypass ignition period, thus posing the problem of thermal damage thereto. Consequently, the above measure is not a practical solution.
With the above-described conventional engine control apparatus, the signal generator 8 generates a crank angle reference signal L.sub.1 which contains only one pulse for one ignition cycle of each cylinder, so the reference crank position for engine control is fixed. As a result, even when the rotational speed of the engine increases during normal engine control, the reference crank position for engine control can not be advanced from the fixed first reference crank position or the rising edge of a first signal pulse (i.e., 75 degrees BTDC). Therefore, the conventional apparatus is not suitable for the high-speed operation of the engine. On the other hand, in order to meet high rotational speeds of the engine, the first reference crank position or the rising edge of a pulse of the crank angle reference signal L.sub.1 has to be set at a certain advanced location. This, however, results in an extended control time such as an extended power supply time during bypass ignition periods. Thus, as referred to above, power consumption increases, generating a large amount of heat. To avoid the resultant thermal destruction of related elements, a heat sink or like heat-absorbing or heat-dissipating means is additionally required. This increases the number of component parts required and makes the overall construction of the apparatus complicated, adding to the costs of manufacture. In addition, the extended control period or duration such as the power supply time results in increased adverse effects on stable engine control due to external disturbances such as sudden variations in the rotational speed of the engine.